This invention relates to a sample dehydration method and apparatus, and more particularly to a sample dehydration method utilizing microwave radiation and an apparatus for practicing the method, and the present invention relates further to an incineration method of a dehydrated sample and an apparatus for performing the same.
Heretofore, a hot-air drying method is extensively employed for drying samples. It is admitted in the art that this method is superior to other methods, such as, for instance, an infrared ray drying method, in the case where it is required to relatively quickly dry samples.
In the hot-air drying method, as is well known in the art, heat energy is applied to only the surface of a sample to be dried, or to be dehydrated. Therefore, the drying time depends on the surface area of the sample, and, accordingly, it takes a relatively long time to dry a sample having a relatively small suface area and low thermal conductivity. In the case where the heat energy applied to the surface area is increased to shorten the time required for drying the sample, a large amount of decomposition gas is produced from the sample, especially when the sample is of an organic material, and therefore a problem of stink takes place, and the sample itself may be destroyed.
For instance, at present, a number of experiment animals are used for a variety of purposes. The used animals, in general, are treated by burning them or burying them in the ground. However, such treatment cannot be allowed in the case where experiment animals have been employed for radioactive experiments. As is well known in the art, the most significant reason for the difficulty encountered in the final treatment of radioactive waste of animals resides in preservation method thereof. Since the waste of animals is liable to be decomposed, the decomposition thereof must be prevented until they are transferred to an authority who takes care of the final treatment thereof. For this purpose, in general, such waste of animals have been preserved by using preservatives such as, for instance, formalin. However, if this method is employed, it will be considerably difficult for the authority to treat them or to burn them, for instance.
Accordingly, the aforementioned troubles will never be caused if the waste of animals can be preserved without using preservatives which usually cause the precessings of the waste of animals to be difficult.
In order to meet this requirement, a method of drying waste of animals can be thought of. However, as was described, the hot-air drying method is disadvantageous in time and decomposition gas. Accordingly, it is very difficult to employ the hot-air drying method. A refrigeration drying method has been also employed to sufficiently dehydrate samples. However, the operations involved in this method are rather troublesome, which is disadvantageous in the point of economical view and in labor saving. Therefore, an effective drying method has been highly desired in various fields including the above mentioned case.
Further, it has been well known that organic sample material possibly containing inorganic substances is sometimes required to be tested for chemical and/or physical analysis of them. For this purpose, incineration of an organic material is a technique which has been employed, as a pretreatment, for analyzing inorganic materials, for a long time. Known in the art are a simple method in which a sample in a crucible or a combustion boat is heated at a high temperature, an oxygen bomb method using a pressure-resisting container, an oxygen flask combustion method, a wet type oxidation method, and so forth. In each of these methods, organic materials are subjected to an oxidation decomposition treatment so that the inorganic materials contained in the organic materials can be readily handled. These methods, however, have common disadvantages in that due to the high temperature utilized, there is a tendency of loss of volatile inorganic substances for example, Hg, As and Pb etc.
The low temperature incineration method using oxygen plasma is a distinctive incineration method developed relatively recently, in which an oxygen gas at a low pressure is excited by high frequency and a plasma gas including atom-like oxygen is brought to be in contact with an organic sample so as to oxidize the organic materials. Accordingly, this method is advantageous in that a loss of a very small amount of metallic elements due to volatilization is substantially eliminated and a quantitative analysis can be achieved without contamination from reagents. Accordingly, the low temperature plasma incineration method has been extensively employed as a pretreatment method for atomic light absorption analysis, colorimetry analysis and electrochemical analysis of food, vegetable samples, vital samples, macromolecular samples, medicines, etc.
However, the incineration rate in the low temperature incineration method is lower than those in other methods, and if the sample is not sufficiently dried in advance, the incineration rate will become much lower. For instance, it takes 30-70 hours to incinerate 2-3 grams of dry intestines of a calf with a frequency of 13.56 MHz, a high frequency output 50 Watts and an oxygen flow rate of 10 ml/min. However, if the sample is not dried, it takes two times as long (cf. a Japanese journal, "Analyzing Equipment" 10, 723 (1972) by Tsuji et al). Therefore, it is essential for improving the incineration efficiency that the sample is sufficiently dehydrated before it is incinerated by an incinerating apparatus. Thus, it is very important to develop a method and apparatus in which the dehydration can be effectively carried out.